Help a not-so-noob: shear stability theory.

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Soooo... 1) using 5w30 as the example, people argue over whether KV100 10cst is better or worse than 9cst (or 9.2 is better than 8.2 in a UOA). KV40 specs are sometimes on PDS's, but we rarely see them on VOA's or UOA's, but in general, to continue with 5w30 example, are generally between upper 50's to 70 (a numerically wider spread than 8 to 9, or even 10). We never see 0C KV spec's do we? Seems 0C would be a useful number, more relevant than -40C specs, except for those poor souls who have to start their engines in N. Dakota winter. But look at how big those visc numbers are at pour point. Us newb-mere-mortals can't even comprehend the difference in the typical numbers. As pointed out above, some 0w30's are "thicker in the middle" than 5w30's, though don't hit the wall at sub-sub-sub freezing Arctic temperatures. It would be nice to know oil specs for 0C, then some some mid-point (and I dont have a problem with 40C), then the "normal" engine temp of 100C. And I don't mean we should take away the readings useful to the Dakotans. 2) taking it the other direction, I've read arguments over HTHS readings of 3.5 or "better" vs 3.1 or "worse." Numerically, a small difference. But seems safe to say, when the "normal engine temp" is 100C, the oil temp in a turbo, or even a main bearing, might be significantly higher. So the closest surrogate I've seen is the HTHS number, but really, how much better is 3.5 compared to 3.1, or 2.9? What delta is really considered significant here? 3) obviously, synthetic vs conventional designation has been smeared so badly, only a handful can make sense of the outlandish performance claims. Thanks to the poster above for explaining how grIV might need less VI treatment than a grpIII, and I guess that was meant to say the grpiV would shear less. But not all synthetics are grpIV.🙁 4) I get the sense, a fair number of people think "modern" oils are less protective than certain older specs (and I don't mean 1970's specs, but say, recent 10w30, 0w40 or 5w40 vs "government-mandated" or government-encouraged 0w20's. Conversely, some equate SN+ to nirvana. Someone comment on how a newb-mere-mortal, such as myself, can differentiate oil quality. And the first person who says, "just use what's in the owners manual," gets the sit-down-and-shut-up buzzer, because that helps no one understand. I love clean air, and non-polluted environments, but for the moment, can we take fuel-economy out of the discussion, and focus on wear protection? Well, it's OK to discuss deposits, varnish, and sludge. For the record, both my vehicles have turbos, and lots of rants about how hard they are on oil (especially the Subaru). But you can find my Ford UOA's, and I don't remember anyone saying, "Gee that ILSAC GF5 GrpIII+ Synthetic sure did great." So I tried the Valvoline PBRestore, and people DID say "gee, that oil did great" but I have no intention of making that my regular fill. Can't afford that, although cheaper than an engine tear down. So still searching for the affordable unicorn oil.
 
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It probably helps to mention the scope of my comments. When most people here mention engine oil as a broad term, they're usually referring to the oils they can easily find on the shelf at Autozone. Those oils only make up about half of my "spectrum" that I base my comments on. The other half includes Amsoil, Red Line, Driven, Schaeffer's, High Performance Lubricants, LAT, and so on. It's correct that PAO is sparingly used in the "common" oils. The common API oils are all within a very small box with only minute differences from brand to brand.
 
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According to most auto manufacturers , the oil selection doesn't matter. we have 3 cars that the owner's manual specifies 5W30 or 10W30 and change the oil for example every 7500 miles ... no mention of the oil type (dino, blend ,syn). Can you expect the same performance using a cheaper dino vs. a good syn after 100K miles? Evidently auto manufacturers do at least for many average cars ...
 
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Originally Posted by OilUzer
According to most auto manufacturers , the oil selection doesn't matter. we have 3 cars that the owner's manual specifies 5W30 or 10W30 and change the oil for example every 7500 miles ... no mention of the oil type (dino, blend ,syn). Can you expect the same performance using a cheaper dino vs. a good syn after 100K miles? Evidently auto manufacturers do at least for many average cars ...
The act of performing maintenance is far more important than the type or brand of oil chosen. The type and brand comes down to wanting a longer than 7500 interval or wanting less friction for better fuel economy or wanting the lowest SAPS possible, etc... The big question for the auto manufacturers is what will ensure the engine will run well for the life of the warranty or 100k miles? Usually once you've passed that mark, they're more interested in selling you a new car than keeping the old one running. Not saying the OEM recommendations can't keep a car alive for 500k+ miles as it certainly can and does in some cases.
 
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Originally Posted by OVERKILL
Yeah, you are completely lost. Let me try and make this a bit clearer: The Winter rating of an oil is simply the oil's ability to pass the CCS and MRV requirements at a given set of temperatures. It has no formal applicable viscosity figure associated with it, just a loose set of limits defined by the SAE. So whether it's a 0w-8 or a 0w-50, all that means is that it was able to pass CCS and MRV at -35C and -40C respectively. ALL oils thicken as they cool. Some 0w-xx's may actually thicken MORE than their 5w-xx counterparts, but will not have the viscosity "wall" that occurs when the waxes in the base oil crystallize, driving up viscosity dramatically and causing it to fail meeting the CCS and MRV requirements for 0w-xx. GENERALLY, the narrower the spread between the Winter rating and the 100C visc, the less VII polymer used in the oil. This is because you need a lighter base oil to meet the lower Winter ratings. This base oil is then "pumped up" with VII to meet the 100C target. HOWEVER, there are exceptions. A lubricant using a PAO base can get away with a heavier base blend and less VII than one using your run of the mill Group III or especially Group II. So if all things were equal (same base used) then the rule holds true, however that's often not the case. XOM for example uses significantly more PAO in many of their 0w-xx products, some being almost entirely PAO-based like their EP and AP 0w-20's, so in this case, these oils, despite the spread, may actually have LESS VII than some cheaper based 5w-20's. Does that make sense?
Sorry for the delay. I didn't post and bail! So I'm still a bit confused, why is it that a lower rating spread (which thins more with heat) is more shear stable? I've reread this post probably ten times, and I don't get it. Is my correlation between thickening/thinning and shear stability just completely wrong? Are they just completely unrelated? shrug I'm genuinely trying to learn, and I feel like the "kid left behind." LOL
 
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Originally Posted by OilStasher
... why is it that a lower rating spread (which thins more with heat) is more shear stable? I've reread this post probably ten times, and I don't get it. Is my correlation between thickening/thinning and shear stability just completely wrong? Are they just completely unrelated? ...
Because, other things being reasonably equal, the low-spread version is less dependent on VI additives to maintain its hot viscosity, and those additives (some of them, anyway) are susceptible to shear damage. That doesn't mean a 5W-30, for example will shear until it's thinner than a 5W-20 of the same brand and line, but means that it might lose a greater percentage of its (higher) original hot viscosity. Thus, the 5W-20 would be more stable.
 
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Originally Posted by CR94
Originally Posted by OilStasher
... why is it that a lower rating spread (which thins more with heat) is more shear stable? I've reread this post probably ten times, and I don't get it. Is my correlation between thickening/thinning and shear stability just completely wrong? Are they just completely unrelated? ...
Because, other things being reasonably equal, the low-spread version is less dependent on VI additives to maintain its hot viscosity, and those additives (some of them, anyway) are susceptible to shear damage. That doesn't mean a 5W-30, for example will shear until it's thinner than a 5W-20 of the same brand and line, but means that it might lose a greater percentage of its (higher) original hot viscosity. Thus, the 5W-20 would be more stable.
Yes, exactly. And its not always the case either, it's just a rough guideline, as base oil selection can play into this.
 
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Shearing in passenger car motor oils has to be on of the most overrated issues on this board. First of all, nearly all the UOA here are from Blackstone who have been shown to not be able to discriminate between mechanical shear and fuel dilution, let alone properly measure viscosity in the first place. So even if you believe that a tested oil has deviated from the initial viscosity there's no way to tell why that happened. Moreover not all viscosity index improvers are equal. That has been discussed many times, some are more shear resistant than others. So blanket statements about multi-viscosity oils does not apply without knowing specifics about the oil under question. In addition the oil molecules themselves (regardless of the Group designation) do not shear as they are far too small to do so. So from that standpoint that's irrelevant. And lastly, the propensity for mechanical shear is highly application dependent. Some engines are more prone to shearing the VII due to their internal design (such as gear-driven camshafts). For the most part there is precious little evidence that actual mechanical shear is anything to worry about for the vast majority of engines and oils on the market.
 
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Originally Posted by CR94
Because, other things being reasonably equal, the low-spread version is less dependent on VI additives to maintain its hot viscosity, and those additives (some of them, anyway) are susceptible to shear damage. That doesn't mean a 5W-30, for example will shear until it's thinner than a 5W-20 of the same brand and line, but means that it might lose a greater percentage of its (higher) original hot viscosity. Thus, the 5W-20 would be more stable.
Ah, this makes a little more sense. So it's not the oil that shears, it's the additives? Hmm. Maybe that's solved. But I think I'm still lost on the "low-spread" (example 5W-20) actually being less of a "spread" than 'high-spread' (example 0W-40). There is less thinning with 0W-40 than 5W-20. Meaning 0W-40 starts moderately thin and doesn't thin much when heated. 5W-20 starts slightly thick and thins a substantial degree down to a 20. Why is 5W-20 less of a spread? That sounds completely backwards to me. It's amazing. The things I've "known" for years suddenly get questioned and I flip my own world upside-down with technicalities. Haha.
 
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Originally Posted by OilStasher
But I think I'm still lost on the "low-spread" (example 5W-20) actually being less of a "spread" than 'high-spread' (example 0W-40). There is less thinning with 0W-40 than 5W-20. Meaning 0W-40 starts moderately thin and doesn't thin much when heated. 5W-20 starts slightly thick and thins a substantial degree down to a 20. Why is 5W-20 less of a spread? That sounds completely backwards to me.
That makes no sense, what are you trying to ask? All oils regardless of grade are very thick when cold and much thinner when hot. No oil goes in the opposite direction.
 
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Originally Posted by OilStasher
Originally Posted by CR94
Because, other things being reasonably equal, the low-spread version is less dependent on VI additives to maintain its hot viscosity, and those additives (some of them, anyway) are susceptible to shear damage. That doesn't mean a 5W-30, for example will shear until it's thinner than a 5W-20 of the same brand and line, but means that it might lose a greater percentage of its (higher) original hot viscosity. Thus, the 5W-20 would be more stable.
Ah, this makes a little more sense. So it's not the oil that shears, it's the additives? Hmm. Maybe that's solved. But I think I'm still lost on the "low-spread" (example 5W-20) actually being less of a "spread" than 'high-spread' (example 0W-40). There is less thinning with 0W-40 than 5W-20. Meaning 0W-40 starts moderately thin and doesn't thin much when heated. 5W-20 starts slightly thick and thins a substantial degree down to a 20. Why is 5W-20 less of a spread? That sounds completely backwards to me. It's amazing. The things I've "known" for years suddenly get questioned and I flip my own world upside-down with technicalities. Haha.
Nope, you are still lost. At 100C, the 0w-40 will be significantly thicker than the 5w-20. The 20 and the 40 represent the ranges for the hot (100C) viscosity of the lubricant. As the temperature drops, both oils will increase in viscosity from that 100C point. At some point near around -30C the 5W-20 will thicken past the limit for the CCS test for a 0w-xx lubricant (6,200cP @ -35C) and thus is unable to hold the 0W Winter designation. Contrarily, the 0w-40, which will actually be thicker above some point approaching this temperature, thickens less here, as its gelation/crystallization point is at a lower temperature, allowing it to attain the 0w-xx Winter designation.
 
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Originally Posted by OVERKILL
Originally Posted by OilStasher
Originally Posted by CR94
Because, other things being reasonably equal, the low-spread version is less dependent on VI additives to maintain its hot viscosity, and those additives (some of them, anyway) are susceptible to shear damage. That doesn't mean a 5W-30, for example will shear until it's thinner than a 5W-20 of the same brand and line, but means that it might lose a greater percentage of its (higher) original hot viscosity. Thus, the 5W-20 would be more stable.
Ah, this makes a little more sense. So it's not the oil that shears, it's the additives? Hmm. Maybe that's solved. But I think I'm still lost on the "low-spread" (example 5W-20) actually being less of a "spread" than 'high-spread' (example 0W-40). There is less thinning with 0W-40 than 5W-20. Meaning 0W-40 starts moderately thin and doesn't thin much when heated. 5W-20 starts slightly thick and thins a substantial degree down to a 20. Why is 5W-20 less of a spread? That sounds completely backwards to me. It's amazing. The things I've "known" for years suddenly get questioned and I flip my own world upside-down with technicalities. Haha.
Nope, you are still lost. At 100C, the 0w-40 will be significantly thicker than the 5w-20. The 20 and the 40 represent the ranges for the hot (100C) viscosity of the lubricant. As the temperature drops, both oils will increase in viscosity from that 100C point. At some point near around -30C the 5W-20 will thicken past the limit for the CCS test for a 0w-xx lubricant (6,200cP @ -35C) and thus is unable to hold the 0W Winter designation. Contrarily, the 0w-40, which will actually be thicker above some point approaching this temperature, thickens less here, as its gelation/crystallization point is at a lower temperature, allowing it to attain the 0w-xx Winter designation.
I completely agree here. Maybe I'm not conveying my point effectively. Let me use a [probably horrible and confusing] analogy. Let's use the alphabet instead of numbers. Let's still use the same viscosity labeling and winter designation method. Let's assume A is thin and Z is thick. But remember oil: in 5W-20, the 5W @0°C is thicker than the 20 @100°C. So I'll have to reverse the alphabet to keep the same rules intact. So in this case I'll say 5W-20 would look like PW-A and 0W-40 would look like MW-G. P(16th letter) minus A(1st letter)=15. So 5W-20 thins 15 'points' when heated. M(13th letter) minus G(7th letter)=6. So 0W-40 thins 6 'points' when heated. 0W-40 thins less. Why is it called the higher spread? That's probably the best explanation of my question I can offer.
 
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Originally Posted by bityw
The 0W-40 is not the "higher spread." The 5W-20 is. I think that's where the confusion is.
It is? Can you explain that please?
 
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Originally Posted by OilStasher
Maybe I'm not conveying my point effectively. Let me use a [probably horrible and confusing] analogy. Let's use the alphabet instead of numbers. Let's still use the same viscosity labeling and winter designation method. Let's assume A is thin and Z is thick. But remember oil: in 5W-20, the 5W @0°C is thicker than the 20 @100°C. So I'll have to reverse the alphabet to keep the same rules intact. So in this case I'll say 5W-20 would look like PW-A and 0W-40 would look like MW-G. P(16th letter) minus A(1st letter)=15. So 5W-20 thins 15 'points' when heated. M(13th letter) minus G(7th letter)=6. So 0W-40 thins 6 'points' when heated. 0W-40 thins less. Why is it called the higher spread? That's probably the best explanation of my question I can offer.
There is no "5W" oil. The ability for an oil to meet (or not meet) the 5W performance specification is largely irrelevant towards and unconnected to the operating viscosity. The winter ratings are performance specifications at the core, not a viscosity. Looking at how an oil thins is looking at the wrong end of the chart if you are discussing the winter rating. At extremely low temperatures the 0W-40 meets the performance specification for a 0W oil whereas the 5W-20 does not, but this is only at a very low temperature. Above that the 5W-20 is always thinner because it is a 20-grade oil and the 0W-40 is a 40-grade. Winter ratings are not confusing nor hard to understand and you don't need letters nor mathematics unless you're deliberately trying to make the situation confusing. You pick the operating viscosity that your engine requires then you pick a winter rating that is appropriate for your expected starting conditions. The only time there is a difference between a 0W and a 5W rated oil is when the starting temperature is well below 0F, somewhere around -35F. If you are starting at temperatures above that then the winter rating is irrelevant.
 
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Originally Posted by OilStasher
completely agree here. Maybe I'm not conveying my point effectively. Let me use a [probably horrible and confusing] analogy. Let's use the alphabet instead of numbers. Let's still use the same viscosity labeling and winter designation method. Let's assume A is thin and Z is thick. But remember oil: in 5W-20, the 5W @0°C is thicker than the 20 @100°C. So I'll have to reverse the alphabet to keep the same rules intact. So in this case I'll say 5W-20 would look like PW-A and 0W-40 would look like MW-G. P(16th letter) minus A(1st letter)=15. So 5W-20 thins 15 'points' when heated. M(13th letter) minus G(7th letter)=6. So 0W-40 thins 6 'points' when heated. 0W-40 thins less. Why is it called the higher spread? That's probably the best explanation of my question I can offer.
I think you are still trying to use the Winter rating as a viscosity number and that's what's confusing you. It's just a pass/fail for a given Winter designation with a set ceiling for both CCS and MRV. It is not related to the hot viscosity.
 
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This threads is a perfect example of why SAE J300 is an outdated way of determining oil viscosity and performance and should be abandoned. CCS-HTHS would eliminate the guesswork... for us at least. It would confuse the [censored] out of 99% of the public. 0w-20 = <6,200 cP @ -35*C, 6.9-9.2 cSt @ 100*C, >2.6 cP @ 150*C 0w-30 = <6,200 cP @ -35*C, 9.3-12.4 cSt @ 100*C, >2.9 cP @ 150*C 0w-40 = <6,200 cP @ -35*C, 12.5-16.2 cSt @ 100*C, >3.5 cP @ 150*C 0w-50 = <6,200 cP @ -35*C, 16.3-21.8 cSt @ 100*C, >3.7 cP @ 150*C 0w-60 = <6,200 cP @ -35*C, 21.9-26.0 cSt @ 100*C, >3.7 cP @ 150*C 5w-20 = <6,600 cP @ -30*C, 6.9-9.2 cSt @ 100*C, >2.6 cP @ 150*C 5w-30 = <6,600 cP @ -30*C, 9.3-12.4 cSt @ 100*C, >2.9 cP @ 150*C 5w-40 = <6,600 cP @ -30*C, 12.5-16.2 cSt @ 100*C, >3.5 cP @ 150*C 5w-50 = <6,600 cP @ -30*C, 16.3-21.8 cSt @ 100*C, >3.7 cP @ 150*C 5w-60 = <6,600 cP @ -30*C, 21.9-26.0 cSt @ 100*C, >3.7 cP @ 150*C 10w-30 = <7,000 cP @ -25*C, 9.3-12.4 cSt @ 100*C, >2.9 cP @ 150*C 10w-40 = <7,000 cP @ -25*C, 12.5-16.2 cSt @ 100*C, >3.5 cP @ 150*C 10w-50 = <7,000 cP @ -25*C, 16.3-21.8 cSt @ 100*C, >3.7 cP @ 150*C 10w-60 = <7,000 cP @ -25*C, 21.9-26.0 cSt @ 100*C, >3.7 cP @ 150*C 15w-30 = <7,000 cP @ -20*C, 9.3-12.4 cSt @ 100*C, >2.9 cP @ 150*C 15w-40 = <7,000 cP @ -20*C, 12.5-16.2 cSt @ 100*C, >3.7 cP @ 150*C 15w-50 = <7,000 cP @ -20*C, 16.3-21.8 cSt @ 100*C, >3.7 cP @ 150*C 15w-60 = <7,000 cP @ -20*C, 21.9-26.0 cSt @ 100*C, >3.7 cP @ 150*C 20w-40 = <9,500 cP @ -15*C, 12.5-16.2 cSt @ 100*C, >3.7 cP @ 150*C 20w-50 = <9,500 cP @ -15*C, 16.3-21.8 cSt @ 100*C, >3.7 cP @ 150*C 20w-60 = <9.500 cP @ -15*C, 21.9-26.0 cSt @ 100*C, >3.7 cP @ 150*C 25w-40 = <13,000 cP @ -10*C, 12.5-16.2 cSt @ 100*C, >3.7 cP @ 150*C 25w-50 = <13,000 cP @ -10*C, 16.3-21.8 cSt @ 100*C, >3.7 cP @ 150*C 25w-60 = <13,000 cP @ -10*C, 21.9-26.0 cSt @ 100*C, >3.7 cP @ 150*C All VIIs shear to some degree, some much more than others. Just because one oil has a wider spread than another with a higher VII content doesn't mean it'll shear more. There are some knowns, but a lot of unknowns unless you're the one formulating the oil. Even then, it can often be a lot of guesswork around budget constraints. There's also other factors such as solubility of VIIs, especially when it comes to oils containing ester. (Ester and VII don't blend well)
 
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Originally Posted by mpack88
So since I bought 0w 20 and 5w 20 RTG oil does that mean the 0w 20 has less VII's and is an actually better oil then the 5w 20?
Two oils from the same family, the 0w-20 will likely have more VII (wider spread on the winter rating). On the other hand, some oils, like M1 AP and EP, use better bases (PAO) to achieve their superior Winter rating, so in those cases, it's quite possible the 0w-20 has less VII. So really, it just depends.
 
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Originally Posted by mpack88
So since I bought 0w 20 and 5w 20 RTG oil does that mean the 0w 20 has less VII's and is an actually better oil then the 5w 20?
Depends.. you would need to know the base oil(s) used and the types and chemistry of the VM's employed. Add to that shearing is a mechanical/physical process, so your particular engine will factor into "the best". Just concern yourself with HTHS. If you want better FE, go with a lower HTHS. If you want better wear protection, go with the one that has the higher HTHS. (a 5w20 and 0w20, even though they're both a SAE20 hot, can have very different hths values). The nice thing is if you can find this data on your favorite lube, HTHS, the lube mfgs have taken much of the guesswork out of thinking for you... freeing you up to do more important things like working on that list of honey do's!...
 
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